This invention relates to a failsafe arrangement intended for use with an actuator, for example a rotary actuator used to drive aircraft flaps between, for example, raised and lowered positions. The failsafe arrangement is also suitable for use with actuators for use in other applications.
Where a rotary actuator is used to drive a flap of an aircraft, it is important to be able to ensure that the movement of a drive shaft used to drive the rotary actuator results in corresponding movement of the flap in order to ensure that the flap is moved to and held in a desired position, in use. In the event of failure of the actuator such that rotary motion of the drive shaft is no longer transmitted to the flap, it is desirable to lock the flap against further movement. The drive shaft is conveniently also locked in position and a signal indicating that a failure has occurred is preferably generated.
U.S. Pat. No. 4,578,993 discloses an actuator including a plurality of gear arrangements driven by a common drive shaft. A ramp/ball arrangement is provided between the outputs of the gear arrangements. In the event of one of the gear arrangements failing, the ramp/ball arrangement operates to lock the outputs of the gear arrangements together. As a result, the actuator may become jammed against further movement and a signal indicative of the failure may be generated.
According to the present invention there is provided a failsafe arrangement comprising a first mounting member, a second mounting member angularly moveable relative to the first mounting member, the first and second mounting members defining first and second surfaces, respectively, which define therebetween a channel, the first and second surfaces being shaped such that the channel is of non-uniform width, at least one wedge member disposed within the channel and carried by a drive member, the wedge member being arranged such that when the drive member and the second mounting member move at the same angular speed, the wedge member does not impair movement of the second mounting member relative to the first mounting member, relative angular movement of the drive member and the second mounting member causing the wedge member to cooperate with the first and second surfaces to apply a braking force, impeding relative angular movement of the first and second mounting members.
Where such an arrangement is used with the actuator for an aircraft flap, the first mounting member is conveniently secured to the aircraft wing, the second mounting member being secured to the flap. The drive member is driven to move at the same rate as the flap in normal use. In the event of the failure of the actuator for the flap, the flap will cease movement whilst the drive member continues to move resulting in the wedge member moving to impede relative movement of the flap and the wing, locking the flap in position.
The first surface is conveniently of circular cross-section, the second surface being of polygonal form. The or each wedge member conveniently comprises a roller. Where the second surface is located radially inward of the first surface, the drive member is conveniently arranged to hold the rollers away from the apices of the second surface during normal operation, movement of the rollers towards the apices of the second surface occurring when relative movement occurs between the drive member and the second mounting member resulting in relative movement of the first and second mounting members being impeded.
The drive member is preferably driven by a drive shaft, an additional wedge member being associated with the drive shaft and arranged to impede rotation of the drive shaft relative to the first mounting member upon failure as described hereinbefore.
The provision of the additional wedge member reduces the risk of the failsafe becoming overloaded.
An indicator is conveniently provided, the indicator being arranged to provide a signal indicative of relative movement having occurred between the drive member and the second mounting member. The indicator may comprise a member carried by the second mounting member and received, at least in part, within a recess provided in the drive member, relative movement of the drive member and second mounting member causing the indicator member to ride out of the recess. The movement of the indicator member may be transmitted to an indicator flag, the movement of the flag away from a rest position providing a visual signal of the presence of a fault condition.